Piezoelectronic device with novel force amplification

ABSTRACT

A piezoelectronic device with novel force amplification includes a first electrode; a piezoelectric layer disposed on the first electrode; a second electrode disposed on the piezoelectric layer; an insulator disposed on the second electrode; a piezoresistive layer disposed on the insulator; a third electrode disposed on the insulator; a fourth electrode disposed on the insulator; a semi-rigid housing surrounding the layers and the electrodes; wherein the semi-rigid housing is in contact with the first, third, and fourth electrodes and the piezoresistive layer; wherein the semi-rigid housing includes a void. The third and fourth electrodes are on the same plane and separated from each other in the transverse direction by a distance.

DOMESTIC PRIORITY

This application is a division of U.S. application Ser. No. 14/577,279filed Dec. 19, 2014, which claims priority to U.S. ProvisionalApplication No. 61/950,343 filed Mar. 10, 2014, the disclosures of whichare incorporated herein by reference in their entirety.

FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with Government support under Contract No.:N66001-11-C-4109 awarded by Defense Advanced Research Projects Agency(DARPA). The Government has certain rights in this invention.

BACKGROUND

The present invention relates to piezotronics, and more specifically, topiezoelectronic devices with force amplification designs.

Piezotronics is a new field of computer technology based on thepiezoelectronic transistor (PET) and variants. In PET operation, apiezoelectric (PE) layer, that expands or contracts with an appliedvoltage, is used to compress a piezoresistive (PR) layer that changesits resistivity upon pressurization. When the PR layer isnon-hysteretic, compression and decompression act as a switch that opensand closes a conductive channel. Three and four terminal switches havebeen described in the prior art (U.S. Pat. Nos. 7,848,135; 8,159,854;8,247,947; and U.S. Patent Publication No. 2013/0009668 A1), along withnew designs for logic that use these switches.

When the PR layer is hysteretic, a period of high compression followedby a partial release can set the resistance to a low and stable value,and a period of low compression and release can set the resistance to ahigh and stable value. Such a device makes a piezoelectronic memory(PEM) cell. PEM using hysteric phase change material has been proposedin the prior art (ELMEGREEN et al., U.S. patent application Ser. No.13/719,965).

A four-terminal PET from the prior art is shown in FIG. 1 for reference.The viewpoint is from the side and fabrication is in layers from thebottom to the top. Two gate electrodes actuate the PE layer, whichexpands and contracts vertically (the z direction) according to thevoltage drop across them. Two sense electrodes straddle the PR layer andsense the resistance across it. These two pairs of electrodes areseparated from each other by an insulator. The current through the PRlayer is along the axis of the device, the same direction as the appliedfield on the PE layer.

A thinner PR layer is advantageous because its internal pressure can beincreased to the required switching pressure with a smaller expansion ofthe PE layer. However a potential disadvantage of the design in theprior art is that the thickness of the PR layer is limited to a fewnanometers by quantum tunneling. Smaller dimensions are likely to haveundesirable leakage currents from quantum tunneling through the PRlayer. Quantum tunneling is also a problem for conventional CMOS FETs.

The present invention proposes solutions to the limitations that areinherent in the prior art.

SUMMARY

According to one embodiment of the present invention, a piezoelectricdevice is provided. The device includes: a first electrode; apiezoelectric layer disposed on the first electrode; a second electrodedisposed on the piezoelectric layer; an insulator disposed on the secondelectrode; a piezoresistive layer, having a top, a bottom, a left, andright side, disposed on the insulator; a third electrode, having a firstportion and a second portion, disposed on the insulator; a fourthelectrode, having a first portion and a second portion, disposed on theinsulator; a semi-rigid housing, having a top, a bottom, and two sides;where the semi-rigid housing surrounds the piezoelectric layer, thepiezoresistive layer, the insulator layer, and the electrodes; where thebottom of the semi-rigid housing is in contact with the first electrodeand the top of the semi-rigid housing is in contact with the third andfourth electrodes and the piezoresistive layer; where between the twosides of the semi-rigid housing and the layers and the electrodes is avoid; where the first and second portion of the third electrode, thefirst and second portion of the fourth electrode, and the piezoresistivelayer each have a yield strength; and where an applied voltage acrossthe first and second electrodes causes a pressure from the piezoelectriclayer to be applied to the piezoresistive layer through the insulatorlayer, such that an electrical resistance of the piezoresistive layer isdependent upon the pressure applied by the piezoelectric layer.

According to a second embodiment of the present invention, apiezoelectric device is provided. The device includes: a first spacinglayer; a second spacing layer; a first electrode disposed on the firstspacing layer; a second electrode disposed on the second spacing layer;a piezoelectric layer, grown with 100 orientation, partially disposed onthe first spacing layer and partially disposed on the second spacinglayer, wherein the piezoelectric layer is disposed between the firstelectrode and the second electrode; an insulator layer disposed on thepiezoelectric layer; a third electrode disposed on the insulator layer;a piezoresistive layer disposed on the third electrode; a fourthelectrode disposed on the piezoresistive layer; a semi-rigid housing,having a top, a bottom, and two sides; where the semi-rigid housingsurrounds the piezoelectric layer, the piezoresistive layer, theinsulator layer, the spacing layers, and the electrodes; where thebottom of the semi-rigid housing is in contact with the first and secondspacing layer, partial contact with the piezoelectric layer; where thetop of the semi-rigid housing is in contact with the fourth electrode;where between the two sides of the semi-rigid housing and the layers andthe electrodes is a void; and where an applied voltage across the firstand second electrodes causes an expansion of the piezoelectric layer inthe transverse direction whereby a pressure from the piezoelectric layeris applied to the piezoresistive layer through the insulator layer, suchthat an electrical resistance of the piezoresistive layer is dependentupon the pressure applied by the piezoelectric layer.

According to a third embodiment of the present invention, apiezoelectric device is provided. The device includes: a first spacinglayer; a second spacing layer; a first electrode disposed on the firstspacing layer; a second electrode disposed on the second spacing layer;a piezoelectric layer, grown with 100 orientation, partially disposed onthe first spacing layer and partially disposed on the second spacinglayer, wherein the piezoelectric layer is disposed between the firstelectrode and the second electrode; an insulator layer disposed on thepiezoelectric layer; a third electrode, having a first portion and asecond portion, disposed on the insulator layer; a piezoresistive layer,having a top, a bottom, a left, and a right side, disposed on theinsulator layer; a fourth electrode, having a first portion and a secondportion, disposed on the insulator layer; a semi-rigid housing, having atop, a bottom and two sides; where the semi-rigid housing surrounds thepiezoelectric layer, the piezoresistive layer, the insulator layer, thespacing layers, and the electrodes; where the bottom of the semi-rigidhousing is in contact with the first and second spacing layers, partialcontact with the piezoelectric layer; where the top of the semi-rigidhousing is in contact with the third and fourth electrodes and thepiezoresistive layer; where between the two sides of the semi-rigidhousing and the layers and the electrodes is a void; where the first andsecond portion of the third electrode, the first and second portion ofthe fourth electrode, and the piezoresistive layer each have a yieldstrength; and where an applied voltage across the first and secondelectrodes causes an expansion of the piezoelectric layer in thetransverse direction whereby a pressure from the piezoelectric layer isapplied to the piezoresistive layer through the insulator layer, suchthat an electrical resistance of the piezoresistive layer is dependentupon the pressure applied by the piezoelectric layer.

According to a fourth embodiment of the present invention, apiezoelectric device is provided. The device includes: a firstelectrode; a piezoelectric layer disposed on the first electrode; asecond electrode disposed on the piezoelectric layer; a piezoresistivelayer disposed on the second electrode, where the second electrode andthe piezoresistive layer have a contact region covering an area;conducting nanoparticles disposed on the piezoresistive layer; where theconducting nanoparticles and the piezoresistive layer have a contactregion covering an area; a third electrode disposed on the conductingnanoparticles; a semi-rigid housing, having a top, a bottom, and twosides; where the semi-rigid housing surrounds the piezoelectric layer,the piezoresistive layer, the conducting nanoparticles, and theelectrodes; where the bottom of the semi-rigid housing is in contactwith the first electrode and the top of the semi-rigid housing is incontact with the third electrode; where between the two sides of thesemi-rigid housing and the layers and the electrodes is a void; andwhere an applied voltage across the first and second electrode causes apressure from the piezoelectric layer to be applied to thepiezoresistive layer, such that an electrical resistance of thepiezoresistive layer is dependent upon the pressure applied by thepiezoelectric layer.

According to a fifth embodiment of the present invention, apiezoelectric device is provided. The device includes: a firstelectrode; a piezoelectric layer disposed on the first electrode; asecond electrode disposed on the piezoelectric layer; conductingnanoparticles disposed on the second electrode; a piezoresistive layerdisposed on the conducting nanoparticles, where the conductingnanoparticles and the piezoresistive layer have a contact regioncovering an area; a third electrode disposed on the piezoresistivelayer, where the third electrode and the piezoresistive layer have acontact region covering an area; a semi-rigid housing, having a top, abottom, and two sides; where the semi-rigid housing surrounds thepiezoelectric layer, the piezoresistive layer, the conductingnanoparticles, and the electrodes; where the bottom of the semi-rigidhousing is in contact with the first electrode and the top of thesemi-rigid housing is in contact with the third electrode; where betweenthe two sides of the semi-rigid housing and the layers and theelectrodes is a void; and where an applied voltage across the first andsecond electrode causes a pressure from the piezoelectric layer to beapplied to the piezoresistive layer, such that an electrical resistanceof the piezoresistive layer is dependent upon the pressure applied bythe piezoelectric layer.

According to a sixth embodiment of the present invention, apiezoelectric device is provided. The device includes: a firstelectrode; a piezoelectric layer disposed on the first electrode; asecond electrode disposed on the piezoelectric layer; a piezoresistivelayer disposed on the second electrode, where the second electrode andthe piezoresistive layer have a contact region covering an area; a thirdelectrode disposed on the piezoresistive layer, where the thirdelectrode and the piezoresistive layer have a contact region covering anarea; a semi-rigid housing, having a top, a bottom, and two sides; wherethe semi-rigid housing surrounds the piezoelectric layer, thepiezoresistive layer, and the electrodes; where the bottom of thesemi-rigid housing is in contact with the first electrode and the top ofthe semi-rigid housing is in contact with the third electrode; wherebetween the two sides of the semi-rigid housing and the layers and theelectrodes is a void; wherein the area of the contact region of thesecond electrode and the piezoresistive layer is either less than orgreater than the area of the contact region of the third electrode andthe piezoresistive layer; and where an applied voltage across the firstand second electrode causes a pressure from the piezoelectric layer tobe applied to the piezoresistive layer, such that an electricalresistance of the piezoresistive layer is dependent upon the pressureapplied by the piezoelectric layer.

According to a seventh embodiment of the present invention, apiezoelectric device is provided. The device includes: a firstelectrode; a piezoelectric layer disposed on the first electrode; asecond electrode disposed on the piezoelectric layer; an insulator layerdisposed on the second electrode; a third electrode disposed on theinsulator layer; conducting nanoparticles disposed on the thirdelectrode; a piezoresistive layer disposed on the conductingnanoparticles, where the conducting nanoparticles and the piezoresistivelayer have a contact region covering an area; a fourth electrodedisposed on the piezoresistive layer, where the fourth electrode and thepiezoresistive layer have a contact region covering an area; asemi-rigid housing, having a top, a bottom, and two sides; where thesemi-rigid housing surrounds the piezoelectric layer, the piezoresistivelayer, the insulator layer, the conducting nanoparticles, and theelectrodes; where the bottom of the semi-rigid housing is in contactwith the first electrode and the top of the semi-rigid housing is incontact with the fourth electrode; where between the two sides of thesemi-rigid housing and the layers and the electrodes is a void; andwhere an applied voltage across the first and second electrodes causes apressure from the piezoelectric layer to be applied to thepiezoresistive layer through the insulator layer, such that anelectrical resistance of the piezoresistive layer is dependent upon thepressure applied by the piezoelectric layer.

According to an eighth embodiment of the present invention, apiezoelectric device is provided. The device includes: a firstelectrode; a piezoelectric layer disposed on the first electrode; asecond electrode disposed on the piezoelectric layer; an insulator layerdisposed on the second electrode; a third electrode disposed on theinsulator layer; a piezoresistive layer disposed on the third electrode,where the third electrode and the piezoresistive layer have a contactregion covering an area; conducting nanoparticles disposed on thepiezoresistive layer, where the conducting nanoparticles and thepiezoresistive layer have a contact region covering an area; a fourthelectrode disposed on the conducting nanoparticles; a semi-rigidhousing, having a top, a bottom, and two sides; wherein the semi-rigidhousing surrounds the piezoelectric layer, the piezoresistive layer, theinsulator layer, the conducting nanoparticles, and the electrodes; wherethe bottom of the semi-rigid housing is in contact with the firstelectrode and the top of the semi-rigid housing is in contact with thefourth electrode; where between the two sides of the semi-rigid housingand the layers and the electrodes is a void; and where an appliedvoltage across the first and second electrodes causes a pressure fromthe piezoelectric layer to be applied to the piezoresistive layerthrough the insulator layer, such that an electrical resistance of thepiezoresistive layer is dependent upon the pressure applied by thepiezoelectric layer.

According to a ninth embodiment of the present invention, apiezoelectric device is provided. The device includes: a firstelectrode; a piezoelectric layer disposed on the first electrode; asecond electrode disposed on the piezoelectric layer; an insulator layerdisposed on the second electrode; a third electrode disposed on theinsulator layer; a piezoresistive layer disposed on the third electrode,where the third electrode and the piezoresistive layer have a contactregion covering an area; a fourth electrode disposed on thepiezoresistive layer, where the fourth electrode and the piezoresistivelayer have a contact region covering an area; a semi-rigid housing,having a top, a bottom, and two sides; where the semi-rigid housingsurrounds the piezoelectric layer, the piezoresistive layer, insulatorlayer, and the electrodes; where the bottom of the semi-rigid housing isin contact with the first electrode and the top of the semi-rigidhousing is in contact with the fourth electrode; where between each ofthe two sides of the semi-rigid housing and the layers and theelectrodes is a void; where the area of the contact region of the thirdelectrode and the piezoresistive layer is either less than or greaterthan the area of the contact region of the fourth electrode and thepiezoresistive layer; and where an applied voltage across the first andsecond electrodes causes a pressure from the piezoelectric layer to beapplied to the piezoresistive layer through the insulator layer, suchthat an electrical resistance of the piezoresistive layer is dependentupon the pressure applied by the piezoelectric layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional diagram of a four-terminalpiezoelectronic transistor (4PET) found in the prior art.

FIG. 2 is a schematic cross-sectional diagram of a 4PET, according to anembodiment of the present invention, showing sense electrodes that wrapa piezoresistive (PR) layer.

FIGS. 3 & 4 are schematic cross-sectional diagrams of three-terminalpiezoelectronic transistors (3PET), according to embodiments of thepresent invention, showing a common electrode and sense electrodes thatwrap the PR layer.

FIG. 5 is a schematic cross-sectional diagram of a 4PET, according to anembodiment of the present invention, where sense electrodes are embeddedin a high yield strength material (HYSM) with additional soft conductorson the sides of the PR layer.

FIG. 6 is a schematic cross-sectional diagram of a 4PET, according to anembodiment of the present invention, where sense electrodes are embeddedin an insulator below the PR layer with soft conductors on the sides ofthe PR layer.

FIG. 7 is a schematic cross-sectional diagram of a 4PET design,according to an embodiment of the present invention, where apiezoelectric (PE) layer is actuated in the transverse direction.

FIG. 8 is a schematic cross-sectional diagram of a 4PET design,according to an embodiment of the present invention, where the PE layeris actuated in the transverse direction and sense electrodes wrap apiezoresistive (PR) layer.

FIG. 9 is a schematic cross-sectional diagram of a 4PET design,according to an embodiment of the present invention, where the PE layeris actuated in the transverse direction and sense electrodes areembedded in a high yield strength material (HYSM) with additional softconductors on the sides of the PR layer.

FIG. 10 is a schematic cross-sectional diagram of a 4PET design,according to an embodiment of the present invention, where the PE layeris actuated in the transverse direction and sense electrodes areembedded in an insulator below the PR layer.

FIGS. 11 & 12 are schematic cross-sectional diagrams of 4PET designs,according to embodiments of the present invention, where the PE layer isactuated in the transverse direction and a conducting nanoparticle islocated between a sense electrode and the PR layer.

FIGS. 13 & 14 are schematic cross-sectional diagrams of 4PET designs,according to embodiments of the present invention, where the PE layer isactuated in the transverse direction and a pointed tip of a senseelectrode is in contact with the PR layer.

FIGS. 15 & 16 are schematic cross-sectional diagrams of 4PET designs,according to embodiments of the present invention, where the PE layer isactuated in the transverse direction and the area of the contact regionbetween one sense electrode and the PR layer is less than the area ofthe contact region between the other sense electrode and the PR layer.

FIG. 17 is a schematic cross-sectional diagram of a three terminalpiezoelectronic transistor (3PET) design, according to an embodiment ofthe present invention, where a conducting nanoparticle is locatedbetween a sense electrode and a piezoresistive (PR) layer.

FIG. 18 is a schematic cross-sectional diagram of a 3PET design,according to an embodiment of the present invention, where a conductingnanoparticle is located between a common electrode and the PR layer.

FIG. 19 is a schematic cross-sectional diagram of a 3PET design,according to an embodiment of the present invention, where a pointed tipof the common electrode is in contact with the PR layer.

FIG. 20 is a schematic cross-sectional diagram of a 3PET design,according to an embodiment of the present invention, where a pointed tipof the sense electrode is in contact with the PR layer.

FIG. 21 is a schematic cross-sectional diagram of a 3PET design,according to an embodiment of the present invention, where the area ofthe contact region between the sense electrode and the PR layer is lessthan the area of the contact region between the common electrode and thePR layer.

FIG. 22 is a schematic cross-sectional diagram of a 3PET design,according to an embodiment of the present invention, where the area ofthe contact region between the common electrode and the PR layer is lessthan the area of the contact region between the sense electrode and thePR layer.

FIGS. 23 & 24 are schematic cross-sectional diagrams of 4PET designs,according to embodiments of the present invention, where a conductingnanoparticle is located between a sense electrode and a piezoresistive(PR) layer.

FIGS. 25 & 26 are schematic cross-sectional diagrams of 4PET designs,according to embodiments of the present invention, where a pointed tipof a sense electrode is in contact with the PR layer.

FIGS. 27 & 28 are schematic cross-sectional diagrams of 4PET designs,according to embodiments of the present invention, where the area of thecontact region between one sense electrode and the PR layer is less thanthe area of the contact region between the other sense electrode and thePR layer.

DETAILED DESCRIPTION

Embodiments of the present invention will now be described below withreference to the accompanying drawings. In the following description,elements that are identical are referenced by the same reference numbersin all the drawings unless noted otherwise. The configurations explainedhere are provided as preferred embodiments, and it should be understoodthat the technical scope of the present invention is not intended to belimited to these embodiments.

FIG. 1 depicts a schematic cross-sectional diagram of a 4PET 100 foundin the prior art. 4PET 100 includes a piezoelectric (PE) layer 106. PElayer 106 is a material that can either expand or contract when anelectric potential is applied across it. PE layer 106 is disposedbetween a first gate electrode 104 and a second gate electrode 108. Alow permittivity insulator layer 110 separates second gate electrode 108from a first sense electrode 112.

Insulator layer 110 separating second gate electrode 108 and first senseelectrode 112 can have a relatively high Young's modulus, such as in therange of 60 gigapascals (GPa) to about 250 GPa, for example, arelatively low dielectric constant (e.g., about 4-12 relative tovacuum), and a high breakdown field. Suitable insulator materials thusinclude, for example, silicon dioxide (SiO₂) or silicon nitride(Si_(x)N_(y)). Further in FIG. 1, a PR layer 114 is disposed betweenfirst sense electrode 112 and a second sense electrode 116. 4PET 100includes a high yield strength material (HYSM) 102, such as silicondioxide (SiO₂) or silicon nitride (Si_(x)N_(y)) that surrounds andencapsulates all of the components described above. There is a gap orvacant space 118 between the various layers of 4PET 100 and the sides ofHYSM 102, which increases the freedom of mechanical displacements of thelayers. The vacant space can also be filled with a gas (e.g., air). Byenclosing the entire device in a HYSM, the pressure exerted by the PElayer on the PR layer is contained. If the device had no HYSM, the PRlayer would move away from the PE layer without significant compressionin the PR layer.

The electrodes in 4PET 100 can include materials such as strontiumruthenium oxide (SrRuO₃ (SRO)), platinum (Pt), tungsten (W) or othersuitable mechanically hard conducting materials. PE layer 106 caninclude a relaxor piezoelectric such as PMN-PT (lead magnesiumniobate-lead titanate) or PZN-PT (lead zinc niobate-lead titanate) orother PE materials typically made from perovskite titanates. Such PEmaterials have a large value of displacement/V d₃₃, e.g., d₃₃=2500 pm/V,support a relatively high piezoelectric strain (˜1%), and have arelatively high endurance, making them ideal for the PET application. PElayer 106 could also include another material such as PZT (leadzirconate titanate). PR layer 114 is a material which undergoes aninsulator-to-metal transition under a relatively low pressure in a rangesuch as 0.4-3.0 GPa. Some examples of PR material include samariumselenide (SmSe), thulium telluride (TmTe), nickel disulfide/diselenide(Ni(S_(x)Se_(1−x))₂), vanadium oxide (V₂O₃) doped with a smallpercentage of Cr, calcium ruthenium oxide (Ca₂RuO₄), etc.

In operation of 4PET 100, an input voltage between first gate electrode104 and second gate electrode 108 can be always positive or zero. Whenthe input voltage is zero, PE layer 106 has no displacement and PR layer114 is uncompressed, giving it a high electrical resistance such that4PET 100 is “off”. When a significant positive voltage is appliedbetween first gate electrode 104 and second gate electrode 108, PE layer106 develops a positive strain. That is, PE layer 106 expands upwardsalong the axis perpendicular to the stack. The upward expansion of PElayer 106 tries to compress insulator layer 110, but the main effect isto compress the more compressible PR layer 114. The compressive actionis effective because the surrounding HYSM 102 strongly constrains therelative motion of the top of second sense electrode 116 and the bottomof first gate electrode 104. The combined effect of the mechanicalcompression of PR layer 114 by the constrained stack and PR layer 114piezoresistive response is to lower first sense electrode 112 to secondsense electrode 116 impedance by about 3-5 orders of magnitude underconditions where the input voltage is the designed line voltage VDD. ThePET switch is now “on.”

The embodiments of the present invention propose PET designs with PRlayer current perpendicular to the PE layer electric field. Theembodiments all solve, in different ways, certain limitations that areinherent in the prior art design of FIG. 1.

According to embodiments of the present invention, the PR layer issensed in a direction perpendicular to its compression, allowing thedistance between the sense electrodes to be much larger than thethickness of the PR layer. This helps to minimize quantum tunneling.

According to embodiments of the present invention, FIG. 2 shows across-sectional diagram of a 4PET 200 where the PR layer has senseelectrodes that control current in the transverse direction. A PE layer106 is disposed on a first gate electrode 104 and a second gateelectrode 108 is disposed on PE layer 106. An insulator layer 110 isthen disposed on second gate electrode 108. A first sense electrode 112,a PR layer 114, and a second sense electrode 116 are then disposed oninsulator layer 110. A HYSM 102 surrounds and encapsulates all of thecomponents described above. Again, there is a gap or vacant space 118between the various layers of the PET and the sides of HYSM 102.

Where FIG. 2 modifies the design of FIG. 1 is in the configuration offirst and second sense electrodes 112 & 116 in relation to PR layer 114.In FIG. 2, first sense electrode 112 and second sense electrode 116share the same plane. A portion of first sense electrode 112 wraps theleft side of PR layer 114 and the remaining portion of first senseelectrode 112 wraps the top side of PR layer 114. A portion of secondsense electrode 116 wraps the right side of PR layer 114 and theremaining portion of second sense electrode 116 wraps the top side of PRlayer 114. The placement of the sense electrodes in this manner allowsfor maximum electrical contact between the PR layer and the senseelectrodes.

The portions of first and second sense electrodes 112 & 116 that wrapthe top of PR layer 114 are separated from each other in the transversedirection by a distance. The top of HYSM 102 separates the senseelectrodes and contacts the top of PR layer at this distance betweenthem. The distance should be large enough that quantum tunneling isminimized (e.g., 4 nm).

Between the top of HYSM 102 and the portions of the first and secondsense electrodes 112 & 116 that wrap the left and right side of PR layer114 there is a gap or void space. As a result, the sense electrodes'resistance to the expansion of the PE layer is minimal.

FIG. 3 depicts a cross-sectional diagram of a 3PET 300, according toembodiments of the present invention. The design in FIG. 3 is amodification to the design in FIG. 2. 3PET 300 initially includes a PElayer 106 disposed on a first gate electrode 104 and a second gateelectrode 108 disposed on PE layer 106. An insulator layer 110 is thendisposed on second gate electrode 108. A first sense electrode 112, a PRlayer 114, and a second sense electrode 116 are then disposed oninsulator layer 110. A HYSM 102 surrounds and encapsulates all of thecomponents described above. Again, there is a gap or vacant space 118between the various layers of the PET and the sides of HYSM 102.However, where 3PET 300 departs from 4PET 200 is that there is aconnection between one of the PR layer sense electrodes and the adjacentPE layer gate electrode, forming a common electrode for the device. Forexample, second sense electrode 116 and second gate electrode 108 form aconnection and result in common electrode 302. Alternatively, a commonelectrode 402 could be formed by a connection between first senseelectrode 112 and second gate electrode 108, as depicted in FIG. 4.

What was once a 4 terminal design in 4PET 200 becomes a 3 terminaldesign in 3PET 300. The arrangement of the components are similar to4PET 200, except now, 3PET 200 includes a PE layer 106 disposed on afirst gate electrode 104 and a common electrode 302 disposed on PE layer106. Insulator layer 110 is disposed on common electrode 302. Firstsense electrode 112 and PR layer 114 are disposed on insulator layer110. A portion of first sense electrode 112 wraps the left side of PRlayer 114 and the remaining portion of first sense electrode 112 wrapsthe top side of PR layer 114. A portion of common electrode 302 wrapsthe right side of insulator layer 110 and the right side of PR layer114. A further portion of common electrode 302 wraps the top side of PRlayer 114.

The portions of first sense electrode 112 and common electrode 302 thatwrap the top side of PR layer 114 are separated from each other in thetransverse direction by a distance, just as in 4PET 200. Again, the topof HYSM 102 separates the sense and common electrodes and contacts thetop of PR layer at the distance between them.

As in 4PET 200, between the top of HYSM 102 and the portions of firstsense electrode 112 and common electrode 302 that wrap the left andright side of PR layer 114 there is a gap or void space.

FIG. 4 depicts a schematic cross-sectional diagram of 3PET 400,according to embodiments of the present invention. The design is analternative design to 3PET 300. The difference between 3PET 300 and 3PET400 are the electrodes that form the common electrode. In 3PET 400,first sense electrode 112 and second gate electrode 108 form aconnection and result in common electrode 402. A portion of second senseelectrode 116 wraps the right side of PR layer 114 and the remainingportion of second sense electrode 116 wraps the top side of PR layer114. A portion of common electrode 402 wraps the left side of insulatorlayer 110 and the left side of PR layer 114. A further portion of commonelectrode 402 wraps the top side of PR layer 114. The other features of3PET 300 are also present in 3PET 400.

FIG. 5 depicts a schematic cross-sectional diagram of a 4PET 500,according to embodiments of the present invention. It is a variation onthe design of 4PET 200. 4PET 500 includes a PE layer 106 disposed on afirst gate electrode 104 and a second gate electrode 108 disposed on PElayer 106. An insulator layer 110 is then disposed on second gateelectrode 108. A PR layer 114 is disposed on insulator layer 110.However, where 4PET 500 departs from 4PET 200 is in the location offirst sense electrode 112 and second sense electrode 116. 4PET 500 alsoadds a first soft conducting layer 502 and a second soft conductinglayer 504 to the design.

In 4PET 500, first soft conducting layer 502 and second soft conductinglayer 504 are disposed on insulator layer 110. First soft conductinglayer 502 is in contact with the left side of PR layer 114. Second softconducting layer 504 is in contact with the right side of PR layer 114.First sense electrode 112 and second sense electrode 116 are embedded inthe top of HYSM 102 that surrounds and encapsulates all of thecomponents described above. Just like in the other PET designsdiscussed, there is a gap or vacant space 118 between the various layersof the PET and the sides of HYSM 102.

First sense electrode 112 contacts both first soft conducting layer 502and the top of PR layer 114. Second sense electrode 116 contacts bothsecond soft conducting layer 504 and the top of PR layer 114. Firstsense electrode 112 and second sense electrode 116 are separated fromeach other in the transverse direction by a distance, just as in FIGS.2-4. Again, the top of HYSM 102 separates the sense electrodes andcontacts the top of the PR layer at the distance between them.

The purpose of soft conducting layers 502 & 504 is to maintainelectrical contact between the sense electrodes and the PR layer in theevent the sense electrodes detach from the PR layer at the contactsurfaces between them. Such a detachment could be caused by metalfatigue in the sense electrodes. As a measure to prevent metal fatigue,the yield strength of first and second soft conducting layers 502 & 504should be smaller than the yield strength of both sense electrodes 112 &116 and PR layer 114.

FIG. 6 depicts a schematic cross-sectional diagram of a 4PET 600,according to embodiments of the present invention. It is a variation onthe design of 4PET 500. 4PET 600 includes a PE layer 106 disposed onfirst gate electrode 104 and second gate electrode 108 disposed on PElayer 106. An insulator layer 110 is then disposed on second gateelectrode 108. However, where 4PET 600 deviates from 4PET 500 is thelocation of sense electrodes 112 & 116.

First sense electrode 112 and second sense electrode 116 are embedded ininsulator layer 110. PR layer 114 is disposed on insulator layer 110 sothat the bottom of PR layer 114 is in contact with first sense electrode112 and second sense electrode 116. First soft conducting layer 502 isdisposed on first sense electrode 112 and second soft conducting layer504 is disposed on second sense electrode 116. First soft conductinglayer 502 contacts the left side of PR layer 114 and second softconducting layer 504 contacts the right side of PR layer 114. The softconducting layers serve the same function as in 4PET 500.

As in FIGS. 2-5, first sense electrode 112 and second sense electrode116 are separated from each other in the transverse direction by adistance to minimize quantum tunneling. Now, insulator layer 110, asopposed to HYSM 102, separates the sense electrodes and contacts thebottom of PR layer at the distance between them.

A HYSM 102 surrounds and encapsulates all of the components describedabove. Again, there is a gap or vacant space 118 between the variouslayers of the PET and the sides of HYSM 102.

The proposed embodiments have a means to amplify the pressure on the PRlayer during expansion of the PE layer through the ratio of adjacentareas. Pressure amplification is important because the PE layer can onlyexert a certain maximum pressure which may not be enough tosignificantly change the resistance in the PR layer.

The minimization of quantum tunneling by separating the sense electrodesfrom each other by a distance in the transverse direction allows for athinner PR layer and therefore a lower voltage and expansion of the PElayer to achieve the same pressure on the PR layer. These transversesensing designs, in FIGS. 2-6, allow the PETs to function as a switch ormemory because resistance changes in the PR layer are independent of thedirection of the compression for materials considered in the prior art.

The designs in FIGS. 2-6 confine the sense current to move through thethin cross-section of the PR layer, which can increase the resistancewhen compared to FIG. 1. Such an increase can be offset by increasingthe width of the PR layer in the third dimension (into the page of thefigures), decreasing the resistivity of the PR layer through the use ofdifferent materials or doping, and/or using a higher PR pressure.

As an alternative or additional measure to prevent metal fatigue in thesense electrodes in FIGS. 2-6 above, the sense electrodes can be coatedwith a thin layer of a hard conducting film. An example of such coatingis in Copper technology, where tantalum is used as a liner material toprotect the Copper from metal fatigue.

The improvement of the designs in FIGS. 2-6 over that in FIG. 1 can beseen from the relationship between pressure, P, voltage, V, and PRthickness, l, which is:P=d ₃₃ V/(1/Y _(PR) +d/Y _(PE))where d₃₃ is the displacement per volt in the PE, d=La/A is a reducedlength equal to the PE thickness L multiplied by the ratio of PR area ato PE area A, and the Y are Young's moduli for the PR and PE. Thisrelationship indicates that a lower PR thickness allows a lower voltageon the PE to give the same PR pressure and resistance drop. For theparameters in the above equation, where A/a=9 or 25, I/L=0.075, andY_(PE)/Y_(PR)=1.5, the voltage for the same P decreases by a factor of0.75 or 0.63, respectively, when the PR thickness decreases from 4 nm to2 nm at the same L. Such a thickness decrease would be undesirable inFIG. 1 because a PR 2 nm thick would have severe quantum tunneling.Alternatively, for the same voltage, the pressure increases by theinverse of these factors at lower PR thickness, and that allows a higherON/OFF ratio for the PET with an exponential sensitivity on P.

If the decreased PR thickness is accompanied by an equal fractionaldecrease in all of the PET dimensions, then d also decreases by the sameamount, and that would allow a factor of 2 lower voltage for the samepressure in the above example.

The impact on the RC time constant would remain the same if theresistivity in the PR is lowered for the new designs. For perpendicularcurrents as in FIG. 1, the resistance in the PR is ρ₁l/a for resistivityρ_(l). For transverse currents as in FIGS. 2-6, the resistance isρ₂w_(x)/(w_(y)l) for width w_(x) in the horizontal direction in thefigure, and width w_(y) into the page. If a=w_(x)w_(y) in FIG. 1, thenthe ratio of the new resistance to the old resistance is(ρ₂/ρ₁)(w_(x)/l)². This ratio is unity if ρ₂/ρ₁=(l/w_(x))²<1. Thecapacitance in the expression for RC time is the capacitance in the PE.If that is unchanged because A and L are unchanged, then the RC time inthe new design will be the same as in FIG. 1 if the resistivity isdecreased by the factor (l/w_(x))², which can be accomplished bymaterial change or doping. If all of the PET dimensions decrease in thesame proportion, a<1, then the RC time for a design like FIG. 1 willdecrease with this proportion if the resistivity does as well. The sameis true for scale changes in the new design. In this case, the sonic andRC frequencies both increase as the inverse of the scaling factor α, thecircuit density increases as 1/a², the voltage decreases as a, and thepower density remains the same.

The embodiments propose designs where the PR layer is sensed in adirection perpendicular to its compression, allowing the distancebetween the sense electrodes to be much larger than the thickness of thePR layer. This helps to minimize quantum tunneling. Further, designs areproposed with arbitrary widths for the PE and PR layers that amplifypressure on the PR layer using a small contact region. Further designsallow for transverse actuation of the PE layer, allowing greaterflexibility to the choice of PE contact area with PR layer.

According to embodiments of the present invention, FIG. 7 shows across-sectional diagram of a 4PET 700 where the PE layer is actuated inthe transverse direction. The design uses the d₃₁ coefficient of the PElayer to drive the PE and PR motions perpendicular to the applied field.The d₃₁ coefficient for displacement per Volt is typically smaller by afactor of 0.4 than the parallel d₃₃ coefficient, but the PR compressioncan still be high if the ratio of the adjacent PE and PR cross-sectionalareas is high (e.g. 25). The PE layer is grown with 100 orientationinstead of with 001 orientation as seen in the prior art.

4PET 700 modifies the design of 4PET 100 by its placement of the firstand second gate electrodes. APE layer 106 is disposed between first gateelectrode 104 and second gate electrode 108. First gate electrode 104wraps the right side of PE layer 106 and second gate electrode 108 wrapsthe left side of PE layer 106. First gate electrode 104 is disposed on afirst soft spacing layer 704 and second gate electrode 108 is disposedon a second soft spacing layer 702. PE layer 106 is partially disposedon both soft spacing layers 702 & 704. An Insulator layer 110 isdisposed on PE layer 106 and separates PE layer 106 from a first senseelectrode 112. A PR layer 114 is disposed between first sense electrode112 and a second sense electrode 116. A HYSM 102 surrounds andencapsulates all of the components described above. There is a gap orvacant space 118 between the various layers of the PET and the sides ofHYSM 102.

Soft spacing layers 702 & 704 partially separate PE layer 106 from thebottom of HYSM 102. This allows for slippage as PE layer 106 expands andcontracts. For this soft spacing layer, dielectrics with elastic modulusless than 10 GPa can be used, for example, organosilicate glass SiCOHfrom plasma enhanced chemical vapor deposition, organic material such aspolyimides, silsesquioxane, benzocyclobutene and aromatic thermosetsfrom spin-on deposition, and many other low dielectric constantmaterials and their porous versions with lower Young's modulus.

The transverse actuation of the PE layer in FIG. 7 provides greaterflexibility to the choice of PE contact area with the PR. In FIG. 1, thecontact area at the first sense electrode is the same as the chargingarea for the PE layer. Increasing the contact area to gain mechanicaladvantage for compression of the PR layer also increases the capacitanceof the PE layer, which slows down the circuit through the RC time. InFIG. 7, the contact areas and the charging areas are independent.

Another embodiment of the present invention builds upon the design inFIG. 7 by arranging the layers of the PET so the PR layer has senseelectrodes that control current in the transverse direction. FIG. 8shows a cross-sectional diagram of a 4PET 800. 4PET 800 includes a PElayer 106 disposed between first gate electrode 104 and second gateelectrode 108. First gate electrode 104 wraps the right side of PE layer106 and second gate electrode 108 wraps the left side of PE layer 106.First gate electrode 104 is disposed on a first soft spacing layer 704and second gate electrode 108 is disposed on a second soft spacing layer702. PE layer 106 is partially disposed on both soft spacing layers 702& 704. An insulator layer 110 is then disposed on PE layer 106. A firstsense electrode 112, a PR layer 114, and a second sense electrode 116are then disposed on insulator layer 110. A HYSM 102 surrounds andencapsulates all of the components described above. Again, there is agap or vacant space 118 between the various layers of the PET and thesides of HYSM 102.

Where FIG. 8 modifies the design of FIG. 7 is in the configuration offirst and second sense electrodes 112 & 116 in relation to PR layer 114.In FIG. 8, first sense electrode 112 and second sense electrode 116share the same plane. A portion of first sense electrode 112 wraps theleft side of PR layer 114 and the remaining portion of first senseelectrode 112 wraps the top side of PR layer 114. A portion of secondsense electrode 116 wraps the right side of PR layer 114 and theremaining portion of second sense electrode 116 wraps the top side of PRlayer 114. The placement of the sense electrodes in this manner allowsfor maximum electrical contact between the PR layer and the senseelectrodes.

The portions of first and second sense electrodes 112 & 116 that wrapthe top of PR layer 114 are separated from each other in the transversedirection by a distance. The top of HYSM 102 separates the senseelectrodes and contacts the top of PR layer at this distance betweenthem. The distance should be large enough that quantum tunneling isminimized (e.g., 4 nm).

Between the top of HYSM 102 and the portions of the first and secondsense electrodes 112 & 116 that wrap the left and right side of PR layer114 there is a gap or void space. As a result, the sense electrodes'resistance to the expansion of the PE layer is minimal.

FIG. 9 depicts a schematic cross-sectional diagram of a 4PET 900,according to embodiments of the present invention. It is a variation onthe design of 4PET 800. 4PET 900 includes a PE layer 106 disposedbetween first gate electrode 104 and second gate electrode 108. Firstgate electrode 104 wraps the right side of PE layer 106 and second gateelectrode 108 wraps the left side of PE layer 106. First gate electrode104 is disposed on a first soft spacing layer 704 and second gateelectrode 108 is disposed on a second soft spacing layer 702. PE layer106 is partially disposed on both soft spacing layers 702 & 704. Aninsulator layer 110 is then disposed on PE layer 106. A PR layer 114 isdisposed on insulator layer 110. However, where 4PET 900 departs from4PET 800 is in the location of first sense electrode 112 and secondsense electrode 116. 4PET 900 also adds a first soft conducting layer902 and a second soft conducting layer 904 to the design.

In 4PET 900, first soft conducting layer 902 and second soft conductinglayer 904 are disposed on insulator layer 110. First soft conductinglayer 902 is in contact with the left side of PR layer 114. Second softconducting layer 904 is in contact with the right side of PR layer 114.First sense electrode 112 and second sense electrode 116 are embedded inthe top of HYSM 102 that surrounds and encapsulates all of thecomponents described above. Just like in the other 4PET designsdiscussed, there is a gap or vacant space 118 between the various layersof the PET and the sides of HYSM 102.

First sense electrode 112 contacts both first soft conducting layer 902and the top of PR layer 114. Second sense electrode 116 contacts bothsecond soft conducting layer 904 and the top of PR layer 114. Firstsense electrode 112 and second sense electrode 116 are separated fromeach other in the transverse direction by a distance, just as in 4PET800. Again, the top of HYSM 102 separates the sense electrodes andcontacts the top of PR layer at the distance between them.

The purpose of soft conducting layers 902 & 904 is to maintainelectrical contact between the sense electrodes and the PR layer in theevent the sense electrodes detach from the PR layer at the contactsurfaces between them. Such a detachment could be caused by metalfatigue in the sense electrodes. As a measure to prevent metal fatigue,the yield strength of first and second soft conducting layers 902 & 904should be smaller than the yield strength of both sense electrodes 112 &116 and PR layer 114.

FIG. 10 depicts a schematic cross-sectional diagram of a 4PET 1000,according to embodiments of the present invention. It is a variation onthe design of 4PET 900. 4PET 1000 includes a PE layer 106 disposedbetween first gate electrode 104 and second gate electrode 108. Firstgate electrode 104 wraps the right side of PE layer 106 and second gateelectrode 108 wraps the left side of PE layer 106. First gate electrode104 is disposed on a first soft spacing layer 704 and second gateelectrode 108 is disposed on a second soft spacing layer 702. PE layer106 is partially disposed on both soft spacing layers 702 & 704. Aninsulator layer 110 is then disposed on PE layer 106. However, where4PET 1000 deviates from 4PET 900 is the location of sense electrodes 112& 116.

First sense electrode 112 and second sense electrode 116 are embedded ininsulator layer 110. PR layer 114 is disposed on insulator layer 110, sothat the bottom of PR layer 114 is in contact with first sense electrode112 and second sense electrode 116. First soft conducting layer 902 isdisposed on first sense electrode 112 and second soft conducting layer904 is disposed on second sense electrode 116. First soft conductinglayer 902 contacts the left side of PR layer 114 and second softconducting layer 904 contacts the right side of PR layer 114. The softconducting layers serve the same function as in 4PET 900.

As in FIGS. 8 & 9, first sense electrode 112 and second sense electrode116 are separated from each other in the transverse direction by adistance to minimize quantum tunneling. Now, insulator layer 110, asopposed to HYSM 102, separates the sense electrodes and contacts thebottom of PR layer at the distance between them.

HYSM 102 surrounds and encapsulates all of the components describedabove. Again, there is a gap or vacant space 118 between the variouslayers of the PET and the sides of HYSM 102.

The minimization of quantum tunneling by separating the sense electrodesfrom each other by a distance in the transverse direction allows for athinner PR layer and therefore a lower voltage and expansion of the PElayer to achieve the same pressure on the PR layer. These transversesensing designs, in FIGS. 8-10, allow the PETs to function as a switchor memory because resistance changes in the PR layer are independent ofthe direction of the compression for materials considered in the priorart.

The designs in FIGS. 8-10 confine the sense current to move through thethin cross-section of the PR layer, which can increase the resistancewhen compared to FIG. 1. Such an increase can be offset by increasingthe width of the PR layer in the third dimension (into the page of thefigures), decreasing the resistivity of the PR layer through the use ofdifferent materials or doping, and/or using a higher PR pressure.

The improvement of the designs in FIGS. 7-10 over that in FIG. 1 can beseen from the relationship between pressure, P, voltage, V, and PRthickness, l, which is:P=d ₃₁ V/(1/Y _(PR) +d/Y _(PE))where d₃₁ is the displacement per volt in the PE, d=La/A is a reducedlength equal to the PE thickness L multiplied by the ratio of PR area ato PE area A, and the Y are Young's moduli for the PR and PE. Thisrelationship indicates that a lower PR thickness allows a lower voltageon the PE to give the same PR pressure and resistance drop. For theparameters in the above equation, where A/a=9 or 25, 1/L=0.075, andY_(PE)/Y_(PR)=1.5, the voltage for the same P decreases by a factor of0.75 or 0.63, respectively, when the PR thickness decreases from 4 nm to2 nm at the same L. Such a thickness decrease would be undesirable inFIG. 1 because a PR 2 nm thick would have severe quantum tunneling.Alternatively, for the same voltage, the pressure increases by theinverse of these factors at lower PR thickness, and that allows a higherON/OFF ratio for the PET with an exponential sensitivity on P.

If the decreased PR thickness is accompanied by an equal fractionaldecrease in all of the PET dimensions, then d also decreases by the sameamount, and that would allow a factor of 2 lower voltage for the samepressure in the above example.

The impact on the RC time constant would remain the same if theresistivity in the PR is lowered for the new designs. For perpendicularcurrents as in FIG. 1, the resistance in the PR is ρ₁l/a for resistivityρ₁. For transverse currents as in FIGS. 8-10, the resistance isρ₂w_(x)/(w_(y)l) for width w_(x) in the horizontal direction in thefigure, and width w_(y) into the page. If a=w_(x)w_(y) in FIG. 1, thenthe ratio of the new resistance to the old resistance is(ρ₂/ρ₁)(w_(x)/l)². This ratio is unity if ρ₂/ρ₁=(l/w_(x))²<1. Thecapacitance in the expression for RC time is the capacitance in the PE.If that is unchanged because A and L are unchanged, then the RC time inthe new design will be the same as in FIG. 1 if the resistivity isdecreased by the factor (l/w_(x))², which can be accomplished bymaterial change or doping. If all of the PET dimensions decrease in thesame proportion, a<1, then the RC time for a design like FIG. 1 willdecrease with this proportion if the resistivity does as well. The sameis true for scale changes in the new design. In this case, the sonic andRC frequencies both increase as the inverse of the scaling factor α, thecircuit density increases as 1/a², the voltage decreases as a, and thepower density remains the same.

FIG. 11 is a schematic cross-sectional diagram of a 4PET 1100, accordingto embodiments of the present invention. The design is a modification of4PET 700 that amplifies the pressure on the PR layer using a smallcontact region. 4PET 1100 includes a PE layer 106 disposed between firstgate electrode 104 and second gate electrode 108. First gate electrode104 wraps the right side of PE layer 106 and second gate electrode 108wraps the left side of PE layer 106. First gate electrode 104 isdisposed on a first soft spacing layer 704 and second gate electrode 108is disposed on a second soft spacing layer 702. PE layer 106 ispartially disposed on both soft spacing layers 702 & 704. An Insulatorlayer 110 is disposed on PE layer 106 and separates PE layer 106 from afirst sense electrode 112. A PR layer 114 is disposed on first senseelectrode 112. A conducting nanoparticle 1102 is disposed between PRlayer 114 and a second sense electrode 116. Conducting nanoparticle 1102acts as a small contact between PR layer 114 and second sense electrode116. The nanoparticle's contact region with the PR layer is smaller thanthe contact region would be between the second sense electrode and thePR layer, if the nanoparticle were not included in the design. Thus, thearea of the contact region between conducting nanoparticle 1102 and PRlayer 114 is less than the area of the contact region between firstsense electrode 112 and PR layer 114. The differing sizes of the area ofthe contact regions with the PR layer results in a pressureamplification on the PR layer when the PE layer expands. Conductingnanoparticle 1102 can be located between PR layer 114 and second senseelectrode 116, as depicted in 4PET 1100, or it can be located betweenfirst sense electrode 112 and PR layer 114, as depicted by 4PET 1200 inFIG. 12. The nanoparticle that was between PR layer 114 and second senselayer 116 in 4PET 1100, is between first sense electrode 112 and PRlayer 114 in 4PET 1200. Other than the location of the nanoparticle, andthus where the force amplification on the PR layer occurs, thecomponents from 4PET 1100 are similarly arranged in 4PET 1200. A HYSM102 surrounds and encapsulates all of the components discussed above.There is a gap or vacant space 118 between the various layers of the PETand the sides of HYSM 102.

FIG. 13 is a schematic cross-sectional diagram of a 4PET 1300, accordingto embodiments of the present invention. The design is a modification of4PET 1100 and 4PET 1200. In 4PET 1300, what differs is the small contactwith the PR layer. In 4PET 1300, first sense electrode 112 has a pointedtip that serves as a small contact with PR layer 114. The pointed tip offirst sense electrode 112 is in contact with PR layer 114. A void spaceor soft material 1302 separates PR layer 114 from the remainder of firstsense electrode 112, so that only the pointed tip is in contact with PRlayer 114. Thus, the area of the contact region between first senseelectrode 112 and PR layer 114 is less than the area of the contactregion between second sense electrode 116 and PR layer 114. Thediffering sizes of the areas of the contact regions with the PR layerresults in a pressure amplification on the PR layer when the PE layerexpands. As an alternative, the small contact with PR layer 114 could bea pointed tip of second sense electrode 116, as depicted by 4PET 1400 inFIG. 14. The void space or soft material 1302 would then separate PRlayer 114 from the remainder of second sense electrode 116, so that onlythe pointed tip is in contact with PR layer 114. Second sense electrode116 is the electrode with the pointed tip in contact with PR layer 114in 4PET 1400, as opposed to first sense electrode 112 in 4PET 1300.Other than which sense electrode has the pointed tip in contact with thePR layer, and thus where the force amplification on the PR layer occurs,the components of 4PET 1400 are similarly arranged as in 4PET 1300. Thepointed tip can be made, for example, by side etching the senseelectrode after it is deposited.

FIG. 15 is yet another variation on localized compression on the PRlayer described in the previous four figures. FIG. 15's depiction of4PET 1500 modifies the small contact region with the PR layer previouslydiscussed. In 4PET 1500, the small contact region with PR layer 114 issecond sense electrode 116. The second sense electrode's contact regionwith the PR layer is smaller than the contact region between the firstsense electrode and the PR layer. Thus, the area of the contact regionbetween second sense electrode 116 and PR layer 114 is less than thearea of the contact region between first sense electrode 112 and PRlayer 114. The differing sizes of the areas of the contact regions withthe PR layer results in a pressure amplification on the PR layer whenthe PE layer expands. The alternative to this design is depicted by 4PET1600 in FIG. 16, where first sense electrode 112 has a small contactregion with PR layer 114. First sense electrode 112 is the electrodewith the smaller contact region with PR layer 114 in 4PET 1600, asopposed to second sense electrode 116 in 4PET 1500. Other than whichsense electrode has the smaller contact region with the PR layer, andthus where the force amplification on the PR layer occurs, thecomponents of 4PET 1600 are similarly arranged as in 4PET 1500.

As depicted in FIGS. 11-16, when one or another contact point on the PRlayer is small, the resistance in the PR will decrease only in thevicinity of the contact region, where the pressure is highest. Thisdecrease in resistivity allows current to flow between the senseelectrodes even in the presence of uncompressed PR layer elsewhere.

The advantage of designs with small contact regions on the PR layer isthat the PE layer can have a small width and still exert a largepressure on the PR. The small PE width maximizes the areal density ofpiezoelectric devices on a chip. The small width of the PE also leads toa small PE capacitance and a small RC time, thereby speeding upoperation.

For example, considering the pressure-voltage equation discussed above,where the area ratio A/a=9 or 25, and for the other variables(l/L=0.075, Y_(PE)/Y_(PR)=1.50, the voltage for a given pressuredecreases by a factor of 0.75 to 0.87 if the PR area is 2 times smaller,and decreases by a factor of 0.63 to 0.80 if the PR area is 4 timessmaller. The actual resistance can be tuned by appropriate choice of thePR material.

As an alternative or additional measure to prevent metal fatigue in thesense electrodes in FIGS. 7-116 above, the sense electrodes can becoated with a thin layer of a hard conducting film. An example of suchcoating is in Copper technology, where tantalum is used as a linermaterial to protect the Copper from metal fatigue.

The proposed embodiments have a means to amplify the pressure on the PRlayer during expansion of the PE layer through the ratio of adjacentareas. Pressure amplification is important because PE layers can onlyexert a certain maximum pressure which may not be enough tosignificantly change the resistance in the PR layer.

The embodiments of the present invention propose three terminal PETdesigns that localize compression in the PR layer. The PE and PR layershave arbitrary widths that amplify the pressure on the PR layer by usinga small contact region. The force from the PE layer is concentrated on asmall region of the PR layer, allowing the PE and PR transversedimensions to be equal for a minimum PET footprint. The designs allsolve, in different ways, certain limitations that are inherent in theprior art design of FIG. 1.

Embodiments of the present invention involve three terminal PET designs.Therefore, the components of the proposed PETs differ slightly thandiscussed above in FIG. 1. Referring to FIG. 17, a cross-sectionaldiagram of a 3PET 1700 is shown. 3PET 1700 includes a PE layer 106disposed on gate electrode 104. A common electrode 1702 is disposed onPE layer 106 and separates it from a PR layer 114. PR layer 114 isdisposed on common electrode 1702. A conducting nanoparticle 1704 isdisposed between PR layer 114 and a sense electrode 116. Conductingnanoparticle 1704 acts as a small contact between PR layer 114 and senseelectrode 116. The nanoparticle's contact region with the PR layer issmaller than the contact region would be between the sense electrode andthe PR layer, if the nanoparticle were not included in the design. Thus,the area of the contact region between conducting nanoparticle 1704 andPR layer 114 is less than the area of the contact region between commonelectrode 1702 and PR layer 114. The differing sizes of the areas of thecontact regions with the PR layers results in pressure amplification onthe PR layer when the PE layers expands. Surrounding and encapsulatingall the components is a HYSM 102. There is a gap or vacant space 118between the various layers of the PET and the sides of HYSM 102.

FIG. 18 is a schematic cross-sectional diagram of a 3PET 1800, accordingto embodiments of the present invention. The design is an alternativeembodiment of 3PET 1700. 3PET 1800 includes all the same components as3PET 1700. The only variation is in relation to the location ofconducting nanoparticle 1704. In 3PET 1800, conducting nanoparticle 1704is disposed between common electrode 1702 and PR layer 114. Senseelectrode 116 is disposed on PR layer 114. Conducting nanoparticle 1704acts as a small contact between common electrode 1702 and PR layer 114.The nanoparticle's contact region with the PR layer is smaller than thecontact region would be between the common electrode and the PR layer,if the nanoparticle were not included in the design. Thus, the area ofthe contact region between conducting nanoparticle 1704 and PR layer 114is less than the area of the contact region between sense electrode 116and PR layer 114. The nanoparticle that was between PR layer 114 andsense electrode 116 in 3PET 1700, is between common electrode 1702 andPR layer 114 in 3PET 1800. Other than the location of the nanoparticle,and thus where the force amplification on the PR layer occurs, thecomponents from 3PET 1700 are similarly arranged in 3PET 1800.

According to another embodiment of the present invention, FIG. 19depicts a schematic cross-sectional diagram of a 3PET 1900. The designinvolves an alternative small contact with the PR layer than theprevious designs. 3PET 1900 includes a similar layout to the other PETsdiscussed. It includes a PE layer 106 disposed on gate electrode 104 anda common electrode 1702 disposed on PE layer 106. A PR layer 114 isdisposed on common electrode 1702. A sense electrode 116 is disposed onPR layer 114. Common electrode 1702 has a pointed tip that serves as asmall contact with PR layer 114. The pointed tip of common electrode1702 is in contact with PR layer 114. A void space or soft material 1902separates PR layer 114 from the remainder of common electrode 1702, sothat only the pointed tip is in contact with PR layer 114. Thus, thearea of the contact region between common electrode 1702 and PR layer114 is less than the area of the contact region between PR layer 114 andsense electrode 116. The differing sizes of the areas of the contactregions with the PR layer results in a pressure amplification on the PRlayer when the PE layers expands. The pointed tip can be made, forexample, by side etching the electrode after it is deposited. As in theprevious PET designs, a HYSM 102 surrounds and encapsulates the PETlayers and a gap or vacant space 118 is between various layers and thesides of HYSM 102.

FIG. 20 shows an alternative embodiment to that in FIG. 19. FIG. 20depicts a cross-sectional diagram of 3PET 2000. 3PET 2000 includes allthe components from 3PET 1900. The only variation relates to theelectrode that has a pointed tip that serves as a small contact with thePR layer. In 3PET 2000, sense electrode 116 has a pointed tip thatserves as a small contact with PR layer 114. The pointed tip of senseelectrode 116 is in contact with PR layer 114. There is a void space orsoft material 1902 that separates PR layer 114 from the remainder ofsense electrode 116, so that only the pointed tip is in contact with PRlayer 114. Thus, the area of the contact region between sense electrode116 and PR layer 114 is less than the areas of the contact regionbetween PR layer 114 and common electrode 1702. Sense electrode 116 isthe electrode with the pointed tip in contact with PR layer 114 in 3PET2000, as opposed to the common electrode 1702 in 3PET 1900. Other thanwhich electrode has the pointed tip in contact with the PR layer, andthus where the force amplification on the PR layers occurs, thecomponents of 3PET 2000 are similarly arranged as in 3PET 1900.

FIG. 21 shows another embodiment where compression is localized in thePR layer. FIG. 21 depicts a cross-sectional diagram of 3PET 2100. Likethe previous PETs, it includes a PE layer 106 disposed on gate electrode104, a common electrode 1702 disposed on PE layer 106, a PR layer 114disposed on common electrode 1702, and a sense electrode 116 disposed onPR layer 114. In 3PET 2100, sense electrode 116 has a small contactregion with PR layer 114. The sense electrode's contact region with thePR layer is smaller than the contact region between the common electrodeand the PR layer. Thus, the area of the contact region between senseelectrode 116 and PR layer 114 is smaller than the area of the contactregion between common electrode 1702 and PR layer 114. The differingsizes of the areas of the contact regions with the PR layers results ina pressure amplification on the PR layer when the PE layer expands. AHYSM 102 encapsulates the layers of the PET and between various layersand the sides of HYSM 102 there is a vacant space or gap 118.

An alternative embodiment to that in FIG. 21 is FIG. 22's diagram of3PET 2200, where the small contact point with PR layer 114 is commonelectrode 1702. In FIG. 22, common electrode 1702 has a small contactregion with PR layer 114. The common electrode's contact region with thePR layer is smaller than the contact region between the sense electrodeand the PR layer. Thus, the area of the contact region between commonelectrode 1702 and PR layer 114 is less than the area of the contactregion between sense electrode 116 and PR layer 114. Common electrode1702 is the electrode with the smaller contact region with PR layer 114in 3PET 2200, as opposed to sense electrode 116 in 3PET 2100. Other thanwhich electrode has the smaller contact region with the PR layer, andthus where the force amplification on the PR layer occurs, thecomponents of 3PET 2200 are similarly arranged as in 3PET 2100.

As depicted in FIGS. 17-22, when one contact point with the PR layer issmall, the resistance in the PR will decrease only in the vicinity ofthe contact point, where the pressure is highest. This decrease inresistivity allows current to flow between the common and senseelectrodes even in the presence of uncompressed PR layer elsewhere.

The advantage of designs with small contact points on the PR layer isthat the PE layer can have a small width and still exert a largepressure on the PR. The small PE width maximizes the areal density ofpiezoelectric devices on a chip. The small width of the PE also leads toa small PE capacitance and a small RC time, thereby speeding up itsoperation.

For example, considering the pressure-voltage equation showing therelationship between pressure, P, voltage, V, and PR thickness, l:P=d ₃₃ V/(l/Y _(PR) +d/Y _(PE))where d₃₃ is the displacement per volt in the PE, d=La/A is a reducedlength equal to the PE thickness L multiplied by the ratio of PR area ato PE area A, and the Y are Young's moduli for the PR and PE. Where thearea ratio A/a=9 or 25, and for the other variables (l/L=0.075,Y_(PE)/Y_(PR)=1.50), the voltage for a given pressure decreases by afactor of 0.75 to 0.87 if the PR area is 2 times smaller, and decreasesby a factor of 0.63 to 0.80 if the PR area is 4 times smaller. Theactual resistance can be tuned by appropriate choice of the PR material.

As an alternative or additional measure to prevent metal fatigue in thesense electrode in FIGS. 17-22 above, the sense electrode can be coatedwith a thin layer of a hard conducting film. An example of such coatingis in Copper technology, where tantalum is used as a liner material toprotect the Copper from metal fatigue.

The proposed embodiments have a means to amplify the pressure on the PRduring expansion of the PE through the ratio of adjacent areas. Pressureamplification is important because PE layers can only exert a certainmaximum pressure which may not be enough to significantly change theresistance in the PR.

The embodiments of the present invention propose PET designs thatlocalize compression in the PR layer. The PE and PR layers havearbitrary widths that amplify the pressure on the PR layer by using asmall contact region. The force from the PE layer is concentrated on asmall region of the PR layer, allowing the PE and PR transversedimensions to be equal for a minimum PET footprint. The designs allsolve, in different ways, certain limitations that are inherent in theprior art design of FIG. 1.

Referring to FIG. 23, a cross-sectional diagram of a 4PET 2300 isprovided. 4PET 2300 includes a PE layer 106 disposed on a first gateelectrode 104, and a second gate electrode 108 disposed on PE layer 106.An insulator layer 110 is disposed on second gate electrode 108 andseparates second gate electrode 108 from a first sense electrode 112. Aconducting nanoparticle 2302 is disposed between a PR layer 114 andfirst sense electrode 112. A second sense electrode 116 is disposed onPR layer 114. Conducting nanoparticle 2302 acts as a small contactbetween PR layer 114 and first sense electrode 112. The nanoparticle'scontact region with the PR layer is smaller than the contact regionwould be between the first sense electrode and the PR layer, if thenanoparticle were not included in the design. Thus, the area of thecontact region between conducting nanoparticle 2302 and PR layer 114 isless than the area of the contact region between second sense electrode116 and PR layer 114. The differing sizes of the areas of the contactregions with the PR layer results in a pressure amplification on the PRlayer when the PE layer expands. Surrounding and encapsulating all thecomponents is a HYSM 102. There is a gap or vacant space 118 betweenvarious layers of the PET and the sides of HYSM 102.

FIG. 24 is a schematic cross-sectional diagram of a 4PET 2400, accordingto embodiments of the present invention. The design is an alternativeembodiment of 4PET 2300. 4PET 2400 includes all the same components as4PET 2300. The only variation is in relation to the location ofconducting nanoparticle 2302. In 4PET 2400, conducting nanoparticle 2302is disposed between PR layer 114 and second sense electrode 116.Conducting nanoparticle 2302 acts as a small contact between PR layer114 and second sense electrode 116. The nanoparticle's contact regionwith the PR layer is smaller than the contact region would be betweenthe second sense electrode and the PR layer, if the nanoparticle werenot included in the design. Thus, the area of the contact region betweenconducting nanoparticle 2302 and PR layer 114 is less than the area ofthe contact region between first sense electrode 112 and PR layer 114.The nanoparticle that was between PR layer 114 and first sense electrode112 in 4PET 2300, is between second sense electrode 116 and PR layer 114in 4PET 2400. Other than the location of the nanoparticle, and thuswhere the force amplification on the PR layer occurs, the componentsfrom 4PET 2300 are similarly arranged in 4PET 2400.

According to another embodiment of the present invention, FIG. 25depicts a schematic cross-sectional diagram of a 4PET 2500. The designinvolves an alternative small contact with the PR layer than theprevious designs. 4PET 2500 includes a similar layout to the other PETsdiscussed. It includes a PE layer 106 disposed on a first gate electrode104, a second gate electrode 108 disposed on PE layer 106, and aninsulator layer 110 disposed on second gate electrode 108. A first senseelectrode 112 is disposed on insulator layer 110. A PR layer 114 isdisposed between first sense electrode 112 and a second sense electrode116. First sense electrode 112 has a pointed tip that serves as a smallcontact with PR layer 114. The pointed tip of first sense electrode 112is in contact with PR layer 114. A void space or soft material 2502separates PR layer 114 from the remainder of first sense electrode 112,so that only the pointed tip is in contact with PR layer 114. Thus, thearea of the contact region between first sense electrode 112 and PRlayer 114 is less than the area of the contact region between secondsense electrode 116 and PR layer 114. The differing sizes of the areasof the contact regions with the PR layer results in a pressureamplification on the PR layer when the PE layer expands. The pointed tipcan be made, for example, by side etching the electrode after it isdeposited. As in the previous PET designs, a HYSM 102 surrounds andencapsulates the layers of the PET and a gap or vacant space 118 isbetween various layers and the sides of HYSM 102.

FIG. 26 shows an alternative embodiment to that in FIG. 25. FIG. 26depicts a cross-sectional layout of 4PET 2600. 4PET 2600 contains allthe components from 4PET 2500. The only variation relates to theelectrode that has a pointed tip in contact with the PR layer. In 4PET2600, second sense electrode 116 has a pointed tip that serves as asmall contact with PR layer 114. The pointed tip of second senseelectrode 116 is in contact with PR layer 114. There is a void space orsoft material 2502 that separates PR layer 114 from the remainder ofsecond sense electrode 116, so that only the pointed tip is in contactwith PR layer 114. Thus, the area of the contact region between secondsense electrode 116 and PR layer 114 is less than the area of thecontact region between first sense electrode 112 and PR layer 114.Second sense electrode 116 is the electrode with the pointed tip incontact with PR layer 114 in 4PET 2600, as opposed to first senseelectrode 112 in 4PET 2500. Other than which sense electrode has thepointed tip in contact with the PR layer, and thus where the forceamplification on the PR layer occurs, the components of 4PET 2600 aresimilarly arranged as in 4PET 2500.

FIG. 27 shows another embodiment where compression is localized in thePR layer. FIG. 27 depicts a cross-sectional diagram of 4PET 2700. Likethe previous PETs, it includes a PE layer 106 disposed on a first gateelectrode 104, a second gate electrode 108 disposed on PE layer 106, aninsulator layer 110 disposed on second gate electrode 108, a first senseelectrode 112 disposed on insulator layer 110, and a PR layer 114disposed between first sense electrode 112 and a second sense electrode116. In 4PET 2700, second sense electrode 116 has a small contact regionwith PR layer 114. The second sense electrode's contact region with thePR layer is smaller than the contact region between the first senseelectrode and the PR layer. Thus, the area of the contact region betweensecond sense electrode 116 and PR layer 114 is less than the area of thecontact region between first sense electrode 112 and PR layer 114. Thediffering sizes of the areas of the contact regions with the PR layerresults in a pressure amplification on the PR layer when the PE layerexpands. A HYSM 102 encapsulates the layers of the PET and betweenvarious layers of the PET and the sides of HYSM 102 there is a vacantspace or gap 118.

An alternative embodiment to that in FIG. 27 in FIG. 28's diagram of4PET 2800, where the small contact region with PR layer 114 is firstsense electrode 112. In FIG. 28, first sense electrode 112 has a smallcontact region with PR layer 114. The first sense electrode's contactregion with the PR layer is smaller than the contact region between thesecond sense electrode and the PR layer. Thus, the area of the contactregion between first sense electrode 112 and PR layer 114 is less thanthe area of the contact region between second sense electrode 116 and PRlayer 114. First sense electrode 112 is the electrode with the smallercontact region with PR layer 114 in 4PET 2800, as opposed to secondsense electrode 116 in 4PET 2700. Other than which sense electrode hasthe smaller contact region with the PR layer, and thus where the forceamplification on the PR layer occurs, the components of 4PET 2800 aresimilarly arranged as in 4PET 2700.

As depicted in FIGS. 23-28, when one contact region on the PR layer issmall, the resistance in the PR will decrease only in the vicinity ofthe contact region, where the pressure is highest. This decrease inresistivity allows current to flow between the sense electrodes even inthe presence of uncompressed PR layer elsewhere.

The advantage of designs with small contact regions on the PR layer isthat the PE layer can have a small width and still exert a largepressure on the PR. The small PE width maximizes the areal density ofpiezoelectric devices on a chip. The small width of the PE also leads toa small PE capacitance and a small RC time, thereby speeding upoperation.

For example, considering the pressure-voltage equation showing therelationship between pressure, P, voltage, V, and PR thickness, l:P=d ₃₃ V/(1/Y _(PR) +d/Y _(PE))where d₃₃ is the displacement per volt in the PE, d=La/A is a reducedlength equal to the PE thickness L multiplied by the ratio of PR area ato PE area A, and the Y are Young's moduli for the PR and PE. Where thearea ratio A/a=9 or 25, and for the other variables (l/L=0.075,Y_(PE)/Y_(PR)=1.50), the voltage for a given pressure decreases by afactor of 0.75 to 0.87 if the PR area is 2 times smaller, and decreasesby a factor of 0.63 to 0.80 if the PR area is 4 times smaller. Theactual resistance can be tuned by appropriate choice of the PR material.

As an alternative or additional measure to prevent metal fatigue in thesense electrodes in FIGS. 23-28 above, the sense electrodes can becoated with a thin layer of a hard conducting film. An example of suchcoating is in Copper technology, where tantalum is used as a linermaterial to protect the Copper from metal fatigue.

The proposed embodiments have a means to amplify the pressure on the PRlayer during expansion of the PE layer through the ratio of adjacentareas. Pressure amplification is important because PE layers can onlyexert a certain maximum pressure which may not be enough tosignificantly change the resistance in the PR layer.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A piezoelectric device, comprising: a firstspacing layer; a second spacing layer; a first electrode disposed on thefirst spacing layer; a second electrode disposed on the second spacinglayer; a piezoelectric layer, grown with 100 orientation, partiallydisposed on the first spacing layer and partially disposed on the secondspacing layer, wherein the piezoelectric layer is disposed between thefirst electrode and the second electrode; an insulator layer disposed onthe piezoelectric layer; a third electrode disposed on the insulatorlayer; a piezoresistive layer disposed on the third electrode; a fourthelectrode disposed on the piezoresistive layer; a semi-rigid housing,having a top, a bottom, and two sides; wherein the semi-rigid housingsurrounds the piezoelectric layer, the piezoresistive layer, theinsulator layer, the spacing layers, and the electrodes; wherein thebottom of the semi-rigid housing is in contact with the first and secondspacing layer, partial contact with the piezoelectric layer; wherein thetop of the semi-rigid housing is in contact with the fourth electrode;wherein between the two sides of the semi-rigid housing and the layersand the electrodes is a void; and wherein an applied voltage across thefirst and second electrodes causes an expansion of the piezoelectriclayer in the transverse direction whereby a pressure from thepiezoelectric layer is applied to the piezoresistive layer through theinsulator layer, such that an electrical resistance of thepiezoresistive layer is dependent upon the pressure applied by thepiezoelectric layer.
 2. The device of claim 1, wherein the third andfourth electrode are coated with a layer of conducting film.
 3. Thedevice of claim 1, wherein: the third electrode and the piezoresistivelayer have a contact region covering an area; the fourth electrode andthe piezoresistive layer have a contact region covering an area; and thearea of the contact region of the third electrode and the piezoresistivelayer is either less than or greater than the area of the contact regionof the fourth electrode and the piezoresistive layer.
 4. The device ofclaim 3, wherein the area of the contact region of the third electrodeand the piezoresistive layer is less than the area of the contact regionof the fourth electrode and the piezoresistive layer.
 5. The device ofclaim 4, further comprising a void space between the third electrode andthe piezoresistive layer adjacent to the area of the contact region ofthe third electrode and the piezoresistive layer.
 6. The device of claim4, further comprising a soft material between the third electrode andthe piezoresistive layer adjacent to the area of the contact region ofthe third electrode and the piezoresistive layer.
 7. The device of claim4, wherein the contact region of the third electrode and thepiezoresistive layer is a pointed tip of the third electrode.
 8. Thedevice of claim 7, wherein the pointed tip of the third electrode pointstoward the piezoresistive layer.
 9. The device of claim 3, wherein thearea of the contact region of the fourth electrode and thepiezoresistive layer is less than the area of the contact region of thethird electrode and the piezoresistive layer.
 10. The device of claim 9,further comprising a void space between the fourth electrode and thepiezoresistive layer adjacent to the area of the contact region of thefourth electrode and the piezoresistive layer.
 11. The device of claim9, further comprising a soft material between the fourth electrode andthe piezoresistive layer adjacent to the area of the contact region ofthe fourth electrode and the piezoresistive layer.
 12. The device ofclaim 9, wherein the contact region of the fourth electrode and thepiezoresistive layer is a pointed tip of the fourth electrode.
 13. Thedevice of claim 12, wherein the pointed tip of the fourth electrodepoints toward the piezoresistive layer.
 14. The device of claim 1,wherein the void between the semi-rigid housing and the first electrodeor the second electrode has a first width and the void between thesemi-rigid housing and the layers including the third electrode and thefourth electrode has a second width.
 15. The device of claim 14, whereinthe first width is less than the second width.